A militia () is generally an army or some other fighting organization of non-professional soldiers, citizens of a country, or subjects of a state, who may perform military service during a time of need, as opposed to a professional force of regular, full-time military personnel; or, historically, to members of a warrior-nobility class (e.g. knights or samurai). Generally unable to hold ground against regular forces, militias commonly support regular troops by skirmishing, holding fortifications, or conducting irregular warfare, instead of undertaking offensive campaigns by themselves. Local civilian laws often limit militias to serve only in their home region, and to serve only for a limited time; this further reduces their use in long military campaigns. Beginning in the late 20th century, some militias (in particular officially recognized and sanctioned militias of a government) act as professional forces, while still being "part-time" or "on-call" organizations. For instance, the members of United States National Guard units are considered professional soldiers, as they...